A motor vehicle in a state of standstill is conventionally prevented from rolling away in that a holding brake is actuated by a vehicle driver either by hand or foot. This activation of the holding brake performed during standstill is an additional measure to be taken by the vehicle driver which is therefore frequently not performed. This may result in a parked motor vehicle rolling away for lack of it having been secured by the holding brake.
In addition, the braking force made available by the holding brake at standstill is directly preset by the vehicle driver. Especially in cases in which the motor vehicle is situated at an ascending or descending slope it is not guaranteed that the braking force of the holding brake generated in this manner is sufficient to keep the motor vehicle in a state of standstill.
It is known from DE-OS-24 20 252 to activate a holding brake of a motor vehicle in response to a position of an accelerator pedal. In this case the holding brake is activated to produce a prefixed braking force when the accelerator pedal is not actuated. It is a drawback in this connection that the braking force generated by the holding brake is prefixed. It can therefore not be suitable to hold the motor vehicle at a standstill at a steep slope, for example. A further drawback is that the holding brake is activated even if the accelerator pedal is not actuated, while the motor vehicle is in an driving mode. This may result in undesired or uncontrollable driving states especially during high vehicle speed, e.g. when a vehicle driver does no longer actuate the accelerator pedal in order to operate the coupling pedal. DE 36 18 532A1, and corresponding U.S. Pat. No. 4,717,207 both of which are incorporated by reference herein, discloses a system in which by means of a valve arranged between a master brake cylinder and wheel brake cylinders of a braking system brake actuating pressure is maintained which is present as a motor vehicle is stopped. By closing the valve the brake actuating pressure preset by the vehicle driver by way of the brake pedal when stopping the vehicle is maintained. In order to detect that the motor vehicle is at a standstill it is checked whether its speed is zero, whether the clutch is released, whether first gear or reverse gear is engaged and whether the angle of inclination of the motor vehicle corresponds to or is greater than a predetermined angle of inclination. If these conditions are fulfilled, the valve is closed and the vehicle driver can release the brake pedal without the brake actuating pressure preset previously being reduced. Here it is of disadvantage that no braking forces are made available at standstill without the brake pedal being actuated when reaching the state of standstill. This is for example the case if the motor vehicle is brought to a standstill without the brake pedal having been actuated. Moreover, it is not possible with this system to generate braking forces required for a standstill when the ignition of the motor vehicle is switched off: